The process explained here will work also for porting into Skyrim armours or outfits made for other games.

As currenly the tools used for modelling are not completely adapted for Skyrim, there are some steps that require some manual adjustments. This will surely change in the future months and this tutorial will be updated when required.

Required tools

Converting an armour to another body for Skyrim

The main steps to adapt an armour or outfit to another body for Skyrim are:

Adapt the armour:

Adapt the _0.nif armour mesh:

Import into Blender the existing armour you want to modify

Import into Blender all parts of the _0.nif body

Adapt the armour's shape

Add a material

Add weights to the armour

Cut parts of the body hidden by the armour

Export the armour

Adjust the armor in Nifskope

Add the armour to the game

Adjust the armour after testing it in game

Adapt the _1.nif armour mesh

Skyrim armour/clothing meshes

Skyrim armour/clothing meshes and character weight

Skyrim has introduced a new feature for characters: the weight slider. You can set the weight of characters or NPCs from 0% (the weight slider is completely to the left) to 100% (the slider is completely to the right).
The changes in the shape of the character are managed using 2 mesh files for each armour/piece of clothing (this also applies to the meshes that contain parts of the body):

With 0% weight, the game uses the _0.nif

With 100% weight, the game uses the _1.nif

With any intermediate weight, the game combines the _0.nif and the _1.nif

An example of this is shown in picture Skyrim armour/clothing meshes and character weight.

This means that you will have to convert two meshes for each of the armours/pieces of cloth instead of only one. In this tutorial we are going to adapt first the _0.nif armour to the new body and once it is finished we will adapt it to the _1.nif body

Adapt the _0.nif armour mesh

Import into Blender the existing armour you want to modify

Editting the NiHeader in NifSkope

Deleting the BSLightingShaderProperty

Importing a mesh into Blender

Deleting the skeleton

Imported mesh without skeleton or body parts

First thing is to import into Blender the meshes of the existing armour or outfit you want to convert to a new body.

As Blender has not yet been fully adapted to Skyrim, to be able to import the nif files into it you have to change some properties in NifSkope. Do the following:

Open the armour you are going to adapt in NifSkope

First step is to edit the NiHeader settings:

In the Block details section, expand the NiHeader property as shown in picture Editting the NiHeader in NifSkope

You'll see that the User version property has a value of 12. Double click on the 12 and then change it to 11.

Then go to the User version 2 property, that has a value of 83. Double click on the 83 and then change it to 34.

Next step is to delete the BSLightingShaderProperty:

Expand the NiTriShape node as shown in picture Deleting the BSLightingShaderProperty

Select the BSLightingShaderProperty node and press Ctrl+Del or right click and select the menu option Block -> Remove Branch

Do this for all the NiTriShape nodes the mesh has (if it has more than one)

Save the modified nif file. This modified nif is the one you will be importing into Blender.

Repeat these steps for all the Skyrim meshes you need to import into Blender.

Note: If you are adapting an existing armour from Oblivion or Fallout you don't need to do the previous steps as those meshes are imported without problems into Blender.

Now you can import the armour into Blender. To do that use the menu option File -> Import -> Netimmerse/Gamebyro (.nif). If you cannot find that option it is because you haven't installed NifScripts. Follow the instructions given here: Installation of Blender to install everything you need.

Once you have all the armour parts imported into Blender:

delete all the skeletons you've imported with the them. To do this, select each skeleton (Scene Root) as shown in picture Deleting the skeleton, press the Delete key and select OK. You have to repeat this process until you have deleted all the skeletons you've imported into Blender. Take into account that each part of the armour you import will bring its own part of the skeleton.

delete all the parts of the armour where the skin is shown: those parts belong to the old body you want to replace with the new one.

Once you've deleted all those, you'll have in Blender only the parts that made the armour, as shown in picture Imported mesh without skeleton or body parts.

Import into Blender all parts of the _0.nif body

Follow the steps explained there and after that you'll end up having in Blender the existing armour plus the body you want to adapt the armour to.

Adapt the armour's shape

You'll see that the existing armour doesn't fit very well the _0 body you've just imported. So you need to adapt the existing armour to the new body: in some places the armour may be too big and in other places too small for the new body, so you have to adjust the shape of the armour.

Things you can do:

You can move vertices of the armour from one position to another.

Note: I find it useful to use the Normal orientation when moving vertices for adapting meshes to other bodies.

You can use the Shrink/Wrap or Scale functionality.

You can hide vertices temporarily when working with the mesh.

You can add new vertices by using funcionalities or modifiers that add new vertices like Subdivide or Subsurf, as they will keep the UVmaps intact.

You can reduce the number of polygons of the existing armour using the Poly Reducer script, as it keeps the UVMaps intact.

Things you cannot do:

You cannot add new vertices or faces by using functionalities like Extrude (if you do, you'll have to redo the UVmaps after that!).

You cannot delete or merge existing vertices.

You cannot use the Decimate modifier to reduce the number of polygons of the existing mesh, as this modifier damages the existing UVmap.

Note: If you need more details on how to use Blender to model 3d objects there are already very good tutorials on the matter like this one: Blender 3d: Noob to pro.

Once you've done adjusting the shape of the armour to the _0 body you can move to the next step.

Add a material

If you have imported an Slyrim armour, as you deleted the BSLightingShaderProperty previously, you'll need to add a material to all the objects that form you armour (included the body parts).
This step is exactly the same as the one explained in Add a material. Follow the process explained there to add a material to your armour and body.

Add weights to the armour

Even though the existing armour already had weights assigned, those were the weights of another body and if you keep them the armour won't move well with the new body as each body has different weights. That's why you have to rebuild completely the weights of the armour.

Cut parts of the body hidden by the armour

Export the armour

Next step is to export the armour from Blender in the nif file format. Follow the process explained here: Export the armour to do it.

Adjust the armour in NifSkope

Again, this step is the same than the one explained in the tutorial about creating a new armour for Skyrim. Just follow the indications given here: Adjust the armour in NifSkope.

Add the armour to the game

If you are converting an armour that already existed in Skyrim to work with another body, most likely you'll want to replace the existing armour with the new one you've adapted. To do that you have to name your mesh like the original one you want to replace, and place it under the same folder.

As an example, let's say that you are adapting the wedding dress to another body, in this case:

place the nif file in the folder Data\meshes\clothes\weddingdress\

rename your nif file to outfit_0.nif

make a copy of your nif file and rename it to outfit_1.nif.

We are going to test first the _0.nif armour mesh. When it works perfectly in game, we will adapt the mesh for the _1 body.
As the _0.nif and _1.nif files of the armour are exactly the same, you will see no changes when you move the weight slider for your character.

Adjust the armour after testing it in game

Adapt the _1.nif armour mesh

Once you have successfully adapted the _0.nif armour mesh to the new body, you can begin working with the conversion of the armour to the corresponding _1.nif body mesh.

Take the _0.nif armour mesh you've just adapted (don't use the existing _1.nif armour mesh for the original body to do this, just workwith your adapted _0.nif armour mesh) and follow the steps explained here: Create the _1.nif armour mesh to adapt it to the new body.

Once the _1.nif armour mesh works fine in game and both armour meshes work fine with the weight slider you are done :)